Feeding Relationships Flashcards

All 25 cards in this deck

What is a trophic level?

A feeding level in a food chain, i.e. the position an organism occupies in that chain.

What is a producer in a food chain?

An organism that makes its own food by photosynthesis, always the first trophic level.
e.g. grass

What name is given to the organism at the second trophic level of a food chain?

The primary consumer (a herbivore).
e.g. the zebra in grass → zebra → tick → oxpecker

In a food chain, what do the arrows represent?

The transfer of energy (and biomass) from the organism eaten to the organism that eats it.

In a predator–prey pair, which organism is the predator?

The one that hunts and eats the other; the prey is the one eaten.
e.g. in rabbit → fox, the fox is the predator

True or false? The arrows in a food chain point from the animal that eats to the food it eats.

False. Arrows point from the food to the consumer, showing the direction energy flows.

What is a food web?

Several interconnected food chains in an ecosystem, showing all the feeding relationships.

What are the steps to predict the effect of removing one species from a food web?
e.g. all foxes are removed from a web where fox eats rabbit and rabbit eats grass

1. Find what the species eats: foxes eat rabbits.
2. Prey increase because fewer are eaten: more rabbits.
3. Follow the effect on: less grass, as more rabbits eat it.

In a food web, what usually happens to a prey population if its predators are removed?

It increases, because fewer prey are eaten/killed so more survive to reproduce.

In a food web, what usually happens to a predator population if its prey population falls?

It decreases, because there is less food available.

True or false? An organism in a food web can belong to more than one trophic level.

True. An omnivore may be a primary consumer in one chain and a secondary consumer in another.

True or false? In a food web, a change in one population only affects the species it directly eats.

False. Effects spread through the web to species that are not directly linked to it.

What is a pyramid of biomass?

A diagram of horizontal bars showing the total dry mass of organisms at each trophic level, drawn to scale.

What are the steps to draw a pyramid of biomass to scale?
e.g. grass $4000$ kg, rabbits $400$ kg, foxes $40$ kg

1. Choose a scale that fits the largest value: $1$ cm $= 1000$ kg.
2. Draw bars of that width, producer at the bottom: $4$ cm, $0.4$ cm, $0.04$ cm.
3. Label each bar with the organism's name.

In a pyramid of biomass, which trophic level is drawn at the bottom?

The producer, and it has the widest bar.

Why is a pyramid of biomass almost always pyramid-shaped?

Biomass decreases at each trophic level because energy and material are lost between levels.

True or false? The bars of a pyramid of biomass can be drawn any length as long as they get smaller going up.

False. The bars must be drawn to scale, in proportion to the biomass values given.

Name four ways energy is lost between one trophic level and the next.

Respiration (heat), movement, excretion and egestion of undigested food.

Apart from respiration and excretion, why is not all of an organism's energy passed to the next trophic level?

Not all of the organism is eaten or digested, e.g. bones, roots and woody parts.

Why are food chains usually limited to about four or five trophic levels?

So much energy is lost at each level that there is too little left to support another level.

Why are there usually fewer organisms at higher trophic levels?

Less energy is available at each level, so it can support fewer (or smaller) organisms.

What is the formula for the percentage efficiency of energy transfer between two trophic levels?

$\text{efficiency} = \dfrac{\text{energy transferred to next level}}{\text{energy available at previous level}} \times 100$

What are the steps to calculate the energy transferred to the next trophic level from a percentage efficiency?
e.g. $200$ kJ in the plants, $10\%$ transferred

1. Divide the percentage by 100: $10 \div 100 = 0.1$.
2. Multiply by the energy available: $200 \times 0.1 = 20$.
3. Give the answer with units: $20$ kJ.

What are the steps to calculate the percentage of biomass lost at a trophic level?
e.g. $500$ kg of plants gives $50$ kg of cattle

1. Find the biomass lost: $500 - 50 = 450$ kg.
2. Divide by the starting biomass: $450 \div 500 = 0.9$.
3. Multiply by 100 and round as asked: $90\%$.

True or false? Energy lost as heat from respiration can be passed on to the next trophic level.

False. Heat energy is lost to the surroundings and cannot be used by the next trophic level.